Theresa May has committed to keeping the Conservatives' target of reducing net migration to the "tens of thousands", saying this represents "sustainable levels".
The Prime Minister said it was important to hit this target given the pressure immigration had put on public services and those on lower incomes.
Mrs May said: "I think it is important that we continue, and we will continue, to say that we do want to bring net migration down to sustainable levels.
"We believe that is the tens of thousands, and of course once we leave the European Union we will have the opportunity to ensure that we have control of our borders here in the UK, because we'll be able to establish our rules for people coming from the European Union into the UK."
Mrs May added: "That's a part of the picture that we haven't been able to control before and we will be able to control it.
"Leaving the EU means that we won't have free movement as it has been in the past."
Conservative sources had earlier said the commitment would appear in the party's General Election manifesto.
Home Secretary Amber Rudd said on Sunday she wanted to "continue to bring immigration down" but stopped short of guaranteeing that David Cameron's controversial target would be repeated.
But last month the Prime Minister - who failed to hit the target as Home Secretary - restated her hope to cut annual net migration to a "sustainable" level in the tens of thousands.
Stephen Martin, director general of the Institute Of Directors, said: "A target is a poor substitute for a proper immigration policy.
"All parties should instead see Brexit as an opportunity to come up with a new system that is good for the economy, but also addresses voters' concerns."
Mr Martin called for better training for young people so they can get jobs in developing industries, as well as the removal of international students from official migration figures.
The latest figures showed net migration dropped to 273,000 in the year to September, the first time in two years the balance of people arriving and leaving the UK dipped below 300,000.
A key part of this was the unexpected fall in the number of international students coming to study in Britain, which dropped to their lowest level since 2002.
Ryan Shorthouse, director of conservative think tank Bright Blue, was also critical of the decision to keep the target.
"Keeping the net migration target is a mistake," he said.
"Controlling migration should not be centred on an arbitrary, indiscriminate and unrealistic figure.
"Instead, Theresa May should introduce realistic, effective and popular ways of controlling migration."
Jeremy Corbyn said Labour would set out its immigration policy next week and said "you're going to have to wait and see" when asked if the party would set a numerical target for net migration.
He promised a "fair" and managed immigration system that "works for all", while pointing out many immigrants have made a "massive contribution" to the NHS, education, industry and public transport services.
On a visit to Worcester, he said: "Theresa May made that promise in 2010 and made the same promise in 2015, and didn't get anywhere near it on any occasion at all.
"Obviously our manifesto will set out our policy when that's produced next week.
"But the issue is that there has to be fair migration into this country and it has to be managed migration."
He dismissed Ukip's "one in, one out" as a "totally unrealistic policy".
"I don't think Ukip have given it any thought whatsoever."